Hoping that anti-obesity drugs will help achieve dramatic weight loss? Not likely, according to a study published in the British Medical Journal. At best, the weight loss will be modest, while many patients will remain significantly obese or overweight.

The study reviewed the effectiveness of three drugs—orlistat, sibutramine and rimonabant—for long term weight loss, and found that weight loss totaled less than 5 kg (11 pounds), or less than 5% of total body weight. The National Institute for Clinical Excellence recommends that use of anti-obesity drugs be stopped if 5% of body weight has not been lost after 3 months.

Changing lifestyle and diet are the recommended initial treatment for obesity, but estimates for anti-obesity drug use in 2005 total $1.2 billion. In the UK, guidelines recommend lifestyle changes combined with drug therapy if a patient’s body mass index is greater than 30.

The findings from 30 placebo-controlled trials were analyzed by the Canadian researchers, with volunteers taking anti-obesity drugs for a year or longer. Their mean weight was 100 kg (15.7 stone), and their mean BMI levels were 35-36. Prof. Raj Padwal and colleagues found orlistat lowered weight by 2.9 kg, sibutramine by 4.2 kg and rimonabant by 4.7 kg. In addition, it was found that patients on weight loss pills were more likely to achieve a 5% — 10% weight loss, than those who took the placebo.

Health benefits linked to drug usage varied. In one trial, orlistat reduced the incidence of diabetes, and all three drugs reduced levels of certain types of cholesterol. Rimonabant increased the risk of depression or anxiety, while adverse effects were noted with all three drugs. The authors recommended trials to examine the incidence of death or disease as a result of taking anti-obesity pills, since none existed at present.

Professor Gareth Williams issued a warning of potential danger if anti-obesity drugs are licensed for sale without prescription, as they already are in the US: “Selling anti-obesity drugs over the counter will perpetuate the myth that obesity can be fixed simply by popping a pill and could further undermine the efforts to promote healthy living, which is the only long term escape from obesity.”

Source: British Medical Journal, November 17, 2007, Vol. 335.